1. Field of the Invention
This invention relates generally to a method and apparatus for use in orthopedic surgical procedures, and more particularly, to a method and apparatus for enabling access to an intramedullary canal of a femur through a femoral knee joint prosthesis.
1. Discussion of the Related Art
A knee joint prosthesis typically comprises a femoral component and a tibial component. The femoral component and the tibial component are designed to be surgically attached to the distal end of the femur and the proximal end of the tibia, respectively. The femoral component is further designed to cooperate with the tibial component in simulating the articulating motion of an anatomical knee joint.
Motion of a natural knee is kinematically complex. During a relatively broad range of flexion and extension, the particular surfaces of a natural knee experiences rotation, medial and lateral angulation, translation in the sagittal plane, rollback and sliding. Knee joint prostheses, in combination with the ligaments and muscles, attempt to allow natural knee motion, as well as absorb and control forces generated during the range of flexion. Depending on the degree of damage or deterioration of the knee tendons and ligaments, it may also be necessary for a knee joint prosthesis to limit one or more of these motions in order to provide adequate stability.
After the knee joint prosthesis is implanted into a patient, there may be situations which require access to the intramedullary canal of the femur, proximal to the femoral component. For example, should a supracondylar fracture occur above the anterior flange of the femur, this fracture may require a femoral nail to provide patient stability. Use of currently available posterior stabilized (PS) femoral components, however, pose various advantages and disadvantages when access to the intramedullary canal is required.
PS femoral components having a "closed box" provide the advantage of preventing debris migration into the articulating joint area, as well as preventing bone cement from passing through the opening to interfere with the tibial component. However, because the top of the box is closed, one way to insert a femoral nail involves removing the PS femoral component, implanting the femoral nail, and reimplanting a new revision PS femoral component. Alternatively, a high speed burr may be used to create a hole through the solid box, thereby creating sharp metal debris that may easily damage the rest of the femoral component.
Should an "open box" PS femoral component be utilized, a femoral nail may be passed through the top of the box and into the intramedullary canal without the disadvantages of the closed box. However, an "open box" PS femoral component also allows increased debris, bone chips or bone cement to pass through into the articulating joint area both during implantation and during use. As such, the use of "open box" or "closed box" PS femoral components each exhibit different advantages and disadvantages.
Another method for assisting in the healing of a supracondylar fracture or to improve patient instability is to modify the knee joint prosthesis with a constrained femoral component. This is generally achieved by providing a femoral component with an intramedullary stem that extends from the box. Here again, with existing stemmed femoral components, the stem is either integral with the femoral component or it must be attached to a modular femoral component before the component is implanted. In such cases, modular knee joint prosthetic devices are available which enables different boxes or different length stems to be coupled to the femoral component. However, these modular knee joint prosthetic devices require assembly before the prosthetic device is implanted and do not allow later intraoperative modification of the knee joint prosthesis without removal of the femoral component itself. This would, therefore, again require the femoral component to be removed with a new revision femoral component being subsequently implanted that has the intramedullary stem.
What is needed then is a method and apparatus for enabling access to an intramedullary canal of a femur through the femoral component of the knee joint prosthesis which does not suffer from the above mentioned disadvantages. This, in turn, will eliminate the need for removal of the femoral component to insert a femoral nail or a femoral stem; provide a closed box which has the advantage of preventing debris or bone cement from entering the articulating joint area; provide an easy mechanism to open the top of the box intraoperatively when it is desired to gain access to the intramedullary canal of the femur without having to remove the femoral component; reduce overall surgical cost, time and complexity to correct a supracondylar fracture; and provide a convertible sealed top which may be subsequently opened after the knee joint prosthesis has been implanted to provide the benefits of both a "closed box" femoral component and an "open box" femoral component. It is, therefore, an object of the present invention to provide such a method and apparatus for enabling access to an intramedullary canal of a femur through a femoral knee joint prosthesis.